Standing wave problem

an aluminum wire of length L1 = 50.0 cm, cross-sectional area 1.00×10-2 cm2, and density 2.70 g/cm3, is joined to a steel wire of density 7.80 g/cm3 and the same cross-sectional area. The compound wire, loaded with a block of m = 10.0 kg, is arranged so that the distance L2 from the joint to the supporting pulley is 44.13 cm. Transverse waves are set up in the wire by using an external source of variable frequency; a node is located at the pulley. Find the lowest frequency of excitation for which standing waves are observed such that the joint in the wire is one of the nodes.

Having some difficulty with this problem. First I calculated the mass and linear density of each section of the rope. Using v^2 = T/u the wavespeed on each section was calculated. However, this gives a different frequency for each section, so I'm obviously doing something wrong. Any suggestions?